Articulated machines, such as wheel loaders, tractor scrapers and trucks have normally used one or more hydraulic cylinders to cause one unit of the articulated machine to articulate with respect to the other unit in order to provide steering. In most of these articulated machines, the hydraulic cylinders are connected between the front and rear units and hydraulic fluid is directed to the respective cylinders to cause extension and retraction thereof. In other articulated machines, the articulation may be performed by the use of a rotary vane motor that is located at the pivot point of the front and rear units and by providing pressurized fluid to one side or the other thereof to cause articulation for steering. In these arrangements, the powered portion of the machine normally requires interrupting the power to at least one of the drive wheels or applying a brake to one of the wheels to initiate steering or articulation of the machine. Likewise, in these arrangements, a differential unit is provided in the drive mechanism in order to allow one wheel to turn at a different rate than the other during steering of the machine. Additionally, most of these units require a differential lock in order to continuously provide power to both wheels when operating in a straight direction.
The present invention is directed to overcoming one or more of the problems as set forth above.